This invention relates generally to electrical discharge machining and more particularly to electrical discharge machining workpieces, such as aircraft engine parts, which have several features machined therein.
Electrical discharge machining (EDM) is a well known process for forming features, such as holes, slots and notches of various shapes and configurations, in an electrically conductive workpiece. Conventional EDM apparatuses typically employ an electrode having the desired shape that is advanced toward the workpiece. A suitable power supply is applied to create an electrical potential between the workpiece and electrode for forming a controlled spark which melts and vaporizes the workpiece material to form the desired feature. The cutting pattern of the electrode is usually computer numerically controlled (CNC) whereby servomotors control the relative positions of the electrode and workpiece. During machining, the electrode and workpiece are immersed in a dielectric fluid, which provides insulation against premature spark discharge, cools the machined area, and flushes away the removed material.
One drawback to electrical discharge machining is that it is a relatively slow process, especially when several distinct features need to be machined into a single workpiece. This is particularly so in the aircraft engine industry where electrical discharge machining is widely used for machining various features into aircraft engine parts. To increase the manufacturing output of such parts, it is common to use an EDM apparatus that machines a number of parts at one time. Such an apparatus has a plurality of work stations, each of which has a workpiece fixture located in a single dielectric tank. The work stations are all typically connected to a common power supply. Thus, machining takes place in series one part at a time. That is, a spark will be created in the first work station and then the next work station and so on until each station has a spark supplied. This sequence is repeated until the machining operation is completed for each workpiece.
A problem with this type of apparatus is that whenever one station gets hung up (i.e., fails to discharge for some reason such as electrode misalignment or a EDM particle remaining in the electrode-workpiece gap) all of the stations will become hung up. And since all stations are stopped, it is not evident which station is causing the stoppage. Furthermore, each station must use the same electrode material and polarity because of the series power connection. Thus, each station machines the same feature into the parts. Parts requiring additional features must then be moved to another machine. This means that multiple machines, fixtures and part handling are required before a part is completed. For example, three operations using three different fixtures would be needed to completely machine a part having three different features. And the tank of dielectric fluid would need to be drained and refilled for each of the three operations as the part is moved from fixture to fixture.
Accordingly, there is a need for an EDM apparatus that more efficiently machines workpieces having multiple features to be machined therein.
The above-mentioned need is met by the present invention which provides an electrical discharge machining apparatus including a single workpiece fixture for holding a workpiece and a plurality of machining heads for machining different features into the workpiece. For example, a first machining head is arranged to machine a first feature into the workpiece, and a second machining head is arranged to machine a second feature into the workpiece.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.